1. Field of the Invention
The present invention relates to the touch technology and, more particularly, to a sensing system and a method for obtaining a location of a pointer thereof.
2. Description of the Related Art
FIG. 1 is a tridimensional view of a conventional sensing system. Referring to FIG. 1, the sensing system 100 is used for sensing a location of a pointer 102. The sensing system 100 includes a reflective mirror 104, light-reflecting elements 106 and 108, an image sensor 110 and a processor 112. The reflective mirror 104, the image sensor 110 and the light-reflecting components 106 and 108 are all disposed on a plane 114. The plane 114 may be a whiteboard. Furthermore, a rectangular area indicated by a label 116 is used as a sensing area of the sensing system 100.
The light-reflecting elements 106 and 108 are both configured for reflecting light to the sensing area 116, and the reflective mirror 104 is configured for generating a mirror image of the sensing area 116. The reflective mirror 104 may be a plane mirror having a mirror surface 118, and the mirror surface 118 faces the sensing area 116. The image sensor 110 is disposed at a corner of the sensing area 116, and has a sensing range covering all of the sensing area 116. The processor 112 is electrically coupled to the image sensor 110 for calculating the location of the point 102 according to an image sensed by the image sensor 110.
FIG. 2 is a schematic view for describing a sensing operation of the sensing system 100. As shown in FIG. 2, a portion below a broken line 202 briefly illustrates a part of the sensing system 100 which can be mirrored by the mirror surface 118; and a portion above the broken line 202 is a mirror image of the part of the sensing system 100, which is generated by the mirror surface 118 mirroring the part of the sensing system 100. In FIG. 2, an object indicated by a label 106′ is a mirror image of the light-reflecting element 106, an object indicated by a label 108′ is a mirror image of the light-reflecting element 108, an object indicated by a label 110′ is a mirror image of the image sensor 110, an area indicated by a label 116′ is a mirror image of the sensing area 116, and an object indicated by a label 102′ is a mirror image of the pointer 102. Thus the image sensor 110 can sense the pointer 102 along a sensing path 204, and also can sense the mirror image 102′ of the pointer 102 along a sensing path 206.
FIG. 3 is a schematic view of the image sensed by the image sensor 110 as shown in FIG. 2. In FIG. 3, a label 300 represents an image-sensing window of the image sensor 110. An oblique-line area indicated by a label 302 is a bright zone with a high luminance formed on the image by the light reflected by the light-reflecting element 106 and the reflective mirror 104. The bright zone 302 is a primary sensing zone. A label 304 represents an obscure line caused by the pointer 102, and a label 306 represents an obscure line caused by the mirror image 102′ of the pointer 102. Therefore, the processor 112 can further calculate the location of the pointer 102 according to locations of the obscure lines 304 and 306 in the image-sensing window 300. A relevant calculating method is disclosed in a Taiwan patent application numbered 097126033.
However, the sensing system 100 has a disadvantage, which will be described in FIG. 4. FIG. 4 illustrates another sensing operation of the sensing system 100. As shown in FIG. 4, when the pointer 102 approaches a boundary 192 of the sensing area 116, although the image sensor 110 is still able to sense the pointer 102 along a sensing path 402 and to sense the mirror image 102′ of the pointer 102 along a sensing path 404, the image sensed by the image sensor 110 may only have a single obscure line appeared therein. This resulted from that the sensing paths 402 and 404 are too close, which will be described in FIG. 5.
FIG. 5 is a schematic view of the image sensed by the image sensor 110 as shown in FIG. 4. As shown in FIG. 5, the obscure line indicated by a label 502 cannot be judged to be the obscure line caused by the pointer 102 or the obscure line caused by the mirror image 102′ of the pointer 102. Thus the location of the pointer 102 calculated by the sensing system 100 may be an error. Furthermore, the sensing system 100 even cannot calculate the location of the pointer 102.